1. Field of the Invention
This invention relates to rubber compositions, and more particularly to a rubber composition having improved reinforcing properties and a low heat build-up.
2. Related Art Statement
In order to meet a social request for saving resources and energy, in a field of rubber industries, particularly tire industry, there has actively been developed pneumatic tires having a low fuel consumption in the last few years. A rubber composition having a low heat build-up is essential to the development of such tires having a low fuel consumption. Particularly, for example, in tires for passenger cars, there is a method of using styrene-butadiene copolymer rubbers (SBR) having the controlled contents of bound styrene and vinyl bond in butadiene unit as described in Japanese Patent laid open Nos. 57-51,503, 57-55,204 and 58-36,705. However, it was entirely impossible to apply this method to rubbers other than SBR, particularly natural rubber which is most widely used in heavy load tires.
On the other hand, in Japanese Patent Application Publication No. 50-38,131, British Pat. No. 1,185,896, U.S. Pat. Nos. 2,315,855 and 2,315,856, and the like, it is known that the heat build-up of rubber compositions is improved by adding nitrosoquinolines, nitrosoanilines and the like thereto. However, these nitroso-compounds surely improve the heat build-up, but have particularly such a drawback that when they are applied to polyisoprene rubbers, the peptizing effect of polymer is large, which considerably degrades reinforcing properties of rubber composition, such as wear resistance and the like.
In the prior art, it was insufficient to satisfy both performances of the reinforcing properties such as wear resistance and the like, and the low heat build-up in the rubber composition composed mainly of natural rubber.